The relation between the geometry and spectroscopic properties of a series of salts of the Cu(I) bis(2,9-dimethyl-1,10-phenanthroline) ion, (Cu-(I)(dmp)(2))(+), is explored. The distortions from the idealized D-2d geometry, which include flattening, rocking of the dmp ligands, and displacement of the Cu atoms out of the dmp planes, show considerable variation, indicating the importance of packing forces in the crystalline environment. The change in the absorption spectra upon flattening of the complex, expressed as the variation of the angle between the dmp planes, which varies from 88degrees in the BF4 and tosylate salts to 73degrees in the picrate, agrees qualitatively with parallel DFT calculations. No correlation is found between ground state geometry and luminescence lifetimes, recorded both at room temperature and at 16 K. The low temperature lifetimes vary by a factor of 8 among the (Cu-(I)(dmp)(2))(+) salts examined, the longest lifetime (2.4 mus at 16 K) being observed for the tosylate salt.